Останови машину перед мостом.

Останови is the imperative form, used for giving a command to one person informally.

• остановить = to stop (dictionary form / infinitive)
• останови = stop!

So in this sentence, Останови машину перед мостом. means a direct command: Stop the car before the bridge.

This imperative comes from the perfective verb остановить, which is very natural when telling someone to complete a single action.

Because машину is in the accusative case, which is used for the direct object of the verb.

Here, the thing being stopped is the car, so машина changes form:

• nominative: машина = car
• accusative: машину = car as the object of the action

This is a very common pattern for feminine nouns ending in -а:

• книга → книгу
• мама → маму
• машина → машину

Because the preposition перед requires the instrumental case.

So:

• мост = bridge (base form)
• мостом = bridge in the instrumental case

After перед, Russian uses instrumental to mean in front of / before something:

• перед домом = in front of the house
• перед школой = in front of the school
• перед мостом = before / in front of the bridge

So the form мостом is there because of the preposition, not because it is the object of the verb.

Here it means in space: before / in front of the bridge.

So the idea is: stop the car at a point before reaching the bridge.

But перед can also be used for time in other contexts:

• перед уроком = before the lesson
• перед обедом = before lunch

In this sentence, because it is about a car and a bridge, the meaning is clearly spatial.

It is both:

• singular: said to one person
• informal: used with someone you address as ты

If you wanted to say the same thing politely or to more than one person, you would use:

Остановите машину перед мостом.

So:

• останови = informal singular
• остановите = polite singular or plural

Russian often uses the perfective imperative when telling someone to do one complete action.

Here, the speaker wants one clear result: the car should come to a stop. That is why останови sounds natural.

The imperfective imperative can exist in other situations, but it often gives a different feel, such as:

• focusing on the process
• repeated action
• general instruction
• sometimes sounding softer or more like be stopping / stop doing this regularly

For a single command with a clear endpoint, останови is the standard choice.

Because останови means stop something, while остановись means stop yourself.

Compare:

• Останови машину. = Stop the car.
• Остановись. = Stop. / Come to a stop.

So if the sentence includes машину, Russian normally uses the non-reflexive verb, because the speaker is telling someone to stop the car as an object.

Yes. Russian word order is more flexible than English because the case endings show the grammatical roles.

The neutral order here is:

Останови машину перед мостом.

But other orders are possible, for example:

• Перед мостом останови машину.
• Машину останови перед мостом.

These alternatives may shift the emphasis:

• Перед мостом first can emphasize where
• Машину first can emphasize what should be stopped

Even though the word order can change, the original version is very natural and straightforward.

The stress is:

останови́ маши́ну пе́ред мосто́м

A rough pronunciation guide:

• останови́ = a-sta-na-VEE
• маши́ну = ma-SHEE-nu
• пе́ред = PYE-ret
• мосто́м = ma-STOM

A few useful notes:

• Unstressed о is often pronounced more like a
• Final voiced consonants are often devoiced, so д in перед sounds closer to t
• Stress matters a lot in Russian, so it is worth learning it together with each word

Usually yes in this kind of sentence, but it is good to notice that Russian перед often has a more physical sense of in front of something.

In driving instructions, перед мостом naturally means:

• before you reach the bridge
• in front of the bridge
• just ahead of the bridge

So the English translation before the bridge is correct, but the Russian phrase strongly fits a physical location.

They break down like this:

• Останови — verb, imperative: the command
• машину — direct object in the accusative case: what should be stopped
• перед мостом — prepositional phrase with instrumental: where to stop it

So the structure is basically:

[Command verb] + [thing affected] + [location]

That is a very common and useful Russian sentence pattern.